A fluid pressure cylinder employed in a clamp device that clamps an object to be clamped, such as a workpiece etc. that is to be subjected to mechining, and that includes a cylinder main body, a piston member that is fitted in the cylinder main body so as to move freely forward and backward therein, and a fluid pressure operation chamber for driving the piston member to at least one of its advance side and its retraction side, is per se known from the prior art.
Now, various rod position detection techniques have been implemented in practice for detecting that the piston member of the fluid pressure cylinder is in its forward limit position in the axial direction, or is in its backward limit position, or is in an intermediate position.
For example, the clamp device of Patent Document #1 detects the position of the piston rod with a pressure sensor that detects the fluid pressure supplied to the fluid pressure cylinder and with a two position sensor that detects a raised position and a lowered position of a detected element on the lower end portion of an operating rod that projects from the piston member of the fluid pressure cylinder to the exterior.
In the clamp device of Patent Document #2, a construction is provided in which a mechanism that operates together with the raising and lowering of an output rod of the fluid pressure cylinder and that opens and closes an air passage is provided externally to one end of the cylinder main body, this mechanism thus being capable of detecting the raised position and the lowered position of the output rod.
And, in the clamp device of Patent Document #3, a workpiece reception stand that receives and supports the object to be clamped is provided independently. The workpiece reception stand comprises a pad member in which an air ejection outlet is formed, and an outer tube member that elastically holds the pad member up toward the object to be clamped. Pressurized air is blown out of the air ejection outlet while the pad member is in a projected position, and, when the clamp device is driven to perform clamping and the pad member is pressed by the object to be clamped and accordingly retracts, the air ejection outlet is blocked by the outer tube member so that the pressure of the pressurized air rises, and the fact that the device has gone into the clamped state is thereby detected.
Patent Document #1: JP Laid Open Pat. Publication 2001-87991.
Patent Document #2: JP Laid Open Pat. Publication 2003-305626.
Patent Document #3: JP Laid Open Pat. Publication 2009-125821.